The invention relates in general to digital signal processing methods for identifying unknown targets and in particular to the use of cepstral coefficients in the identification method.
Digital signal processing is used in a wide variety of applications directed to identifying unknown targets. While the precise identity of the unknown target is not known, one assumes that the unknown target is one of a group of known targets. Therefore, digital templates or signatures of known targets are created first. Then, a signal from an unknown target is received and processed. The signature of the unknown target is compared with the signatures of the known targets. The unknown target is identified as the known target having the signature that best matches the signature of the unknown target. The unknown target may be passive or active. The signal may be electromagnetic or acoustic. If the unknown target is passive, it is radiated with a signal and the reflected signal is processed.
This general method has been used in, for example, voice recognition and military target recognition applications. In the military environment, a particular area of interest is Non-Cooperative Target Identification (NCTI). NCTI systems are a valuable piece of the combat identification puzzle. NCTI exploits the physical attributes of targets of interest by using the principles of physics, without intentional participation of the target. Known systems are signals returning from the Radar Signal Modulation (RSM) phenomenon to process and extract signatures that support recognition of types of targets.
In some cases, however, the unknown target signal cannot be matched with a known target signal. Ambiguity may exist due to the similarity of physical attributes between some targets of interest. Some targets differ only in two major areas: their low order features, which are not easily discernable using existing NCTI technology due to low signal to noise ratio (SNR); and/or their frequencies, which are a function of time (varying with time). Thus, there is a need for an improved method of identifying targets.